@Brian Peters. Thanks for your comments about mediating the songs - I take your point.

I guess with the older collectors changing a song with an 'antiquarian' or 'folklorist' hat on is different to making them into songs for contemporary singers.

Most of the mediating I have been the recipient of is album cover notes and performers introductions. I wonder how much of the background information associated with the older collections is essential packaging ("tell us something about this song") and marketing hype ("Ancient..., Relics of...") rather than deeply meaningful theorising.